Existing anti-reflection glasses are known to exhibit a lower level of transmittance after being stored in a salt fog chamber for extended periods of time (e.g., five days at 35° C., 5% NaCl and a pH of between 6.5 and 7.2). It is also known that anti-reflection glass products can eventually fail during such tests due to the presence of partial or whole pealed films that have a lower resistance to sodium hydroxide (NaOH), particularly under conditions of high moisture and elevated temperatures over extended periods of time.
It has now been found that the durability and transmittance of anti-reflection glass can be significantly improved (even during extended salt fog chamber tests) by introducing tin oxide (e.g., SnO2) nanoparticles (e.g., 10-20 nm in size) which have more stable chemical properties into the coating formulation for the anti-reflection glass. SnO2 is an n-type semiconductor with a wide band gap, e.g., 3.6 eV at 300° K, and thus possesses unique optical and electrical properties, including variable receptivity in gaseous environments, high optical transparency in the visible range (up to 97%), low resistivity (4 to 106 Ωcm−1) and excellent chemical stability.
In certain example embodiments of this invention, there is provided a method of forming a coated article comprising an anti-reflection coating on a glass substrate to increase transmittance, the method comprising: providing a colloidal solution comprising tin oxide based nanoparticles; depositing at least a portion of said colloidal solution comprising tin oxide based nanoparticles on a glass substrate to form a substantially uniform coating; curing said coating at least by heating said glass substrate and said coating.
It has been found that matte/matte anti-reflection glass products having two different coating layers (e.g., SnO2 nanoparticles on the “rough” side and silica (SiO2) nanoparticles on the “smooth side”) show and increase in transmittance (ΔTqe %) of the anti-reflection glass of at least about 2%, more preferably at least about 3.5%. The observed increase of Tqe % using SnO2 nanoparticles is believed to be the result of a different pore structure in the final coating. As high as a 30% increase in Tqe % has also been observed for anti-reflection matte/matte glass coated with SnO2 nanoparticles after being exposed in a salt fog chamber for a period of 5 days. Those improved results during a salt fog test may be due to the formation of a more crystalline form of SnO2 in the film.